1. Field of the Invention
The present invention relates to a fan motor having a small thickness and its blades formed to have a tooth structure or chamfers at the edge ends.
2. Description of the Related Art
As notebook PCs and other apparatuses have become increasingly thinner, they are expected to become much thinner in the future. Accordingly, cooling devices that will be used in notebook PCs, such as fan motors, will also be required to be much thinner. However, as notebook PCs become thinner, the temperature inside the housing increases and the ventilation efficiency decreases as the width of blades for dissipation of heat to the outside becomes narrow. As a possible method to earn a negative pressure area for extra space produced from the results of making a blade width thinner, there is a technique of making a length of the blade in a diametrical direction longer.
As a fan motor to be mounted on a notebook PC for heat dissipation, a fan motor having a small thickness is used, which has a multi-blade centrifugal impeller to integrally rotate with a motor's rotor of a motor within a housing.
A multi-blade centrifugal fan such as a sirocco fan has an airflow structure in which an air current is created by a centrifugal force from the center to an outer circumferential direction. To improve the ventilation efficiency, a sawtoothed structure 42 is provided at edge ends of inner and outer peripheries of a blade 41 in an axial direction, as shown in FIG. 13 (for example, refer to Japanese Patent Application Publication No. Hei-11-141494 (FIG. 4, FIG. 5), or a plurality of annular plates are stacked at an outer periphery of an impeller in a predetermined pitch, (for example, refer to Japanese Patent Application Publication No. Hei-10-306795 (FIG. 1 to FIG. 5)) to reduce aerodynamic noises produced by trailing vortex of the rear edge end-side of the blade.